The present invention relates to electrostatically actuated devices and more particularly to silicon-based actuators having a corrugated, multi-layer silicon membrane structure for increased rigidity.
Cross-reference is made to co-pending application U.S. Pat. Nos. 6,357,865, 6,467,879, and U.S. patent application Ser. No. 09/768,676 entitled xe2x80x9cElectrostatically-Acutated Device Having A Corrugated Multi-Layer Membrane Structurexe2x80x9d filed concurrently herewith, the entire disclosure of which is hereby incorporated by reference.
In ink-jet printing, droplets of ink are selectively ejected from a plurality of drop ejectors in a printhead. The ejectors are operated in accordance with digital instructions to create a desired image on a print medium moving past the printhead. The printhead may move back and forth relative to the sheet in a typewriter fashion, or in the linear array may be of a size extending across the entire width of a sheet, to place the image on a sheet in a single pass.
The ejectors typically comprise actuators connected to both a nozzle or drop ejection aperture and to one or more common ink supply manifolds. Ink is retained within each channel until there is a response by the actuator to an appropriate signal. In one embodiment of the ejector, the ink drop is ejected by the pressure transient due to volume displacement of an electrostatically- or magnetostatically-actuated deformable membrane, which typically is a capacitor structure with a flexible electrode, fixed counter electrode, and actuated by a voltage bias between the two electrodes.
Silicon-based actuators can also be employed in micro-electromechanical devices that can be used for pumping and switching, and wherein for example, silicon based actuators are, respectively, used for microfluid pumping, and optical switching. Fluids are pumped due to the volume displacement of an electrostatically- or magnetostatically-deformable membrane, which is a capacitor structure with a flexible electrode, fixed counter electrode, and actuated by a voltage bias between the two silicon electrodes. Optical switching occurs by the displacement of optical elements as a result of actuation due to electrostatic or magnetostatic interactions with other on-chip elements or a magnetostatic device package. For example, in optical switching a mirror can be employed as the optical element using electrostatic actuators to provide the displacement.
This capacitor structure which incorporates a deformable membrane for these silicon-based actuators can be fabricated in a standard polysilicon surface micro-machining process. It can be batch fabricated at low cost using existing silicon foundry capabilities. The surface micro-machining process has proven to be compatible with integrated microelectronics, allowing for the monolithic integration of the actuation with associated addressing electronics.
A problem associated with using such devices as actuators in ink jet printing is that to generate the pressure required for ejecting ink drops from the print head, the membrane must be sufficiently rigid. Apart from increasing the membrane thickness or using stiffer material, which may not be allowed in a standardized surface-micromachining fabrication process, one solution is to make the membrane smaller. However, as the membrane shrinks, so does the displacement volume, and thus the size of the drop emitted. Therefore, it is desirable to increase the ink jet drop ejector ability to eject useful-sized drops of ink without decreasing the size of the ejector or increasing the thickness of the membranes.
A method for fabricating a membrane having a corrugated, multi-layer structure, comprising the steps of: providing a substrate having an insulator layer on the top surface of the substrate, a conductive layer on the insulator layer, a sacrificial layer on said conductive layer, and a second conductive layer; patterning a series of holes the second conductive layer to allow release etchant to have access to a second sacrificial layer; depositing the second sacrificial layer onto said second conductive layer so that the series of holes are filled with the second sacrificial layer; patterning the second sacrificial layer with a radial and/or concentric grid pattern so that a third conductive layer when deposited will form the support structure and top portion of the corrugated structure; depositing the third conductive layer so that the grid pattern is filled in and is in contact with the second conductive layer; removing the first and second sacrificial layer by immersing the device in a release etchant.
These and other aspects of the invention will become apparent from the following description, the description being used to illustrate a preferred embodiment of the invention when read in conjunction with the accompanying drawings.